[EN] CATALYTIC ASYMMETRIC SYNTHESIS OF OPTICALLY ACTIVE alpha-HALO-CARBONYL COMPOUNDS<br/>[FR] SYNTHESE ASYMETRIQUE CATALYTIQUE DE COMPOSES DE DOLLAR G(A)-HALO-CARBONYLE OPTIQUEMENT ACTIFS
申请人:HALLAND NIS
公开号:WO2005080298A1
公开(公告)日:2005-09-01
A process for the catalytic asymmetric synthesis of an optically active compound of the formula (la) or (lb): wherein R is an organic group; X is halogen; Rl and R2which may the same or different represents H, or an organic group or Rl and R2 may be bridged together forming part of a ring system; R and R2 may be bridged together forming part of a ring system; with the provisio that R and Rl are different and R2, when different from H, is attached though a carbon-carbon bond, comprising the step of reacting a compound of the formula (2): with a halogenation agent in the presence of a catalytic amount of a chiral nitrogen containing organic compound.
The enantioselective aminocatalytic α-chlorination of aldehydes is a challenging reaction because of its tendency to proceed through neutral intermediates in unselective pathways. Herein we report the rational shift to a highly selective reaction pathway involving charged intermediates using hexafluoroisopropanol as solvent. This change in mechanism has enabled us to match and improve upon the yields
The direct organocatalytic enantioselective α-chlorination of aldehydes has been developed. The reaction proceeds for a series of different aldehydes with NCS as the chlorine source using easily available catalysts such as l-proline amide and (2R,5R)-diphenylpyrrolidine. The α-chloro aldehydes are obtained in up to 99% yield and up to 95% ee. The synthetic utility of the enantioselective α-chlorination